Over the last decade the medical procedure known as angioplasty has become widely accepted as a safe and effective method for treating various types of vascular diseases. For example, angioplasty is widely used for opening stenoses throughout the vascular system and particularly for opening stenoses in coronary arteries. At present, the most common form of coronary angioplasty is called percutaneous transluminal coronary angioplasty (PTCA). This procedure utilizes an elongate more or less flexible dilatation catheter having an inflatable balloon at its distal end. Using a fluoroscope and radiopaque dyes for visualization, a physician may steer the distal end of the dilatation catheter into position through a guide catheter and across the stenosis. Once so positioned, the dilatation balloon is inflated for a brief duration to open the artery and establish adequate blood flow.
Typically, inflation of the balloon is accomplished by supplying pressurized fluid through an inflation lumen in the catheter. This inflation lumen is connected to an inflation apparatus, which includes a source of pressurized inflation fluid and is located outside the patient's body. Conversely, applying a negative pressure to the inflation lumen collapses the balloon to its minimum dimension for removal of the balloon catheter from within the target blood vessel. Such an application of negative pressure to the dilatation balloon is also used to insure that the balloon has its minimal dimensions during insertion of the balloon to a treatment site.
In the past years a number of balloon catheter designs have been developed which have contributed to the safety and acceptability of PTCA and similar medical procedures. The most common design is known as an "over-the-wire" balloon catheter. This conventional dual-lumen device typically utilizes a relatively large lumen for passage of a guide wire and injection of angiographic visualization dye to assist in the placement of the device. A second parallel lumen is provided for inflation and deflation of the balloon. Typically, a steerable guide wire is positioned within the larger lumen and the entire assembly is maneuvered into an initial position within the target artery through a previously positioned guide catheter having an inner diameter of appropriately larger size sufficient to pass the treatment catheter. Once near the site of the stenoses, the guide wire can be rotated and axially extended or retracted into position across the lesion. The balloon dilatation catheter is subsequently advanced along the guide wire to position its deflated balloon across the lesion. Inflation of the balloon effects dilation of the stenosis.
Though successful at opening stenotic lesions, these dual-lumen catheters are relatively bulky and stiff, which makes their use difficult for any lesions except those that are proximal and localized in non-tortuous, easily accessible vessels. Moreover, these over-the-wire balloon catheters are of an early design, and require an additional implanting physician or assistant to control the guide wire during positioning of the assembly because movement of the catheter and guide wire are independent of one another. This complex coordinated activity requires both experience and skill, and may also result in a slower insertion procedure than is desired.
An alternative over-the-wire catheter assembly utilizes a non-removable guide wire that allows for longitudinal or axial movement. However, this design has a significant drawback because the entire non-removable guide wire catheter assembly must be removed to accomplish replacement or exchange of the balloon. In some cases of PTCA it is necessary to replace the balloon with one of different diameter or configuration following the initial dilation. Additionally, cases of acute re-closure have been noted where the lesion re-closes following dilation and removal of the balloon catheter. This alternative over-the-wire system adds to the difficulties of these subsequent procedures by requiring that the replacement catheter renegotiate the entire placement vascular path without the advantage of a retained guide wire position. That is, when the catheter is pulled out to allow a catheter exchange, the path to the treatment site is at least partially lost because the guide wire comes out with the catheter assembly.
Another version of conventional balloon dilatation catheters are known as, "mono-rail" variants of the standard balloon-on-a-wire system, and have been developed so that only a distal portion of the balloon catheter tracks over the guide wire. These mono-rail catheter systems utilize a conventional inflation lumen and a relatively short guiding or through lumen for the guide wire at the distal end of the catheter. The principal benefits of the mono-rail variant of balloon dilatation catheter is the reduction of frictional drag over the length of the guide wire, which is external of the catheter over much of the length of the catheter, and the ease of balloon exchange. The mono-rail catheters provide the ability to recross an acutely closed vessel or to exchange balloons without removing or extending the guide wire. However, a disadvantage of this design is the increased difficulty in steering the guide wire because this guide wire is not supported by the balloon catheter itself. Additionally, the mono-rail catheters are at least of dual lumen configuration at their distal ends, and this design produces a larger profile for the catheter and a larger shaft size.
Another conventional balloon dilatation catheter design is the "fixed-wire" or integrated "balloon-on-a-wire" dilatation catheter. These single-lumen designs utilize a relatively small guide wire diameter positioned within an inflation lumen and permanently fixed to the distal end of the dilatation balloon. This design produces a low-profile assembly which is able to cross severely narrowed lesions and to navigate tortuous vascular pathways. Additionally, the fixed guide wire is bonded at the distal end of the balloon, and improves the steerability and pushability of these designs. This aspect of the fixed-wire catheters also enhances their maneuverability. The thin shaft design of these catheters also improves coronary visualization, and enables all but the tightest critical lesions to be crossed. However, although able to provide relatively quick and simple balloon placement, as well as providing access to lesions otherwise unsuitable for PTCA, balloon-on-a-wire systems sacrifice both the ability to maintain guide wire position across the lesion when exchanging balloons, and also the safety advantage of being able to recross an acutely closed vessel without repositioning the entire assembly.